I see schtroumpfs?

What puzzles me is the different UT2003 servers: sometimes all the guys are blue?? Why? Am I blue too? They kill me really fast! And what is AntiTCC? I see in the server list something like "3 netspeed changes allowed" - what's that?

And why are so many servers locked? Do I need some kind of an invitation or what?

The reason all the other guys are blue is the server is probably forcing team skins. This is where all players are automatically red or blue, and prevents players from using a dark skin to hide in shadows and get the upper hand in fights.

AntiTCC is a hack protection/security used by servers to prevent cheats from entering.

I don't know about the netspeed thing.

Locked servers are private servers. Usually a clan server or LAN server, where the admins dont want general public players from entering. There should still be plenty of public (open) servers that you can join.

The netspeed changes mean that you are allowed to change your netspeed 3 times on this server / round. Afaik, some people used constantly changing netspeed settings to cheat, this setting in AntiTCC prevents that.

If they looked like this then it was a server running TTM, a mutator for more 'competitive' gameplay with brightskins and hitsounds and stuff.
Probably they were all blue or red because it was DM in TDM there would have been a blue and a red team.